Large-Scale Combinatorial Deorphanization of Platynereis Neuropeptide GPCRs

Abstract

Neuropeptides, representing the largest class of neuromodulators, commonly signal by G-protein-coupled receptors (GPCRs). While the neuropeptide repertoire of several metazoans has been characterized, many GPCRs are orphans. Here, we develop a strategy to identify GPCR-peptide pairs using combinatorial screening with complex peptide mixtures. We screened 126 neuropeptides against 87 GPCRs of the annelid Platynereis and identified ligands for 19 receptors. We assigned many GPCRs to known families and identified conserved families of achatin, FMRFamide, RGWamide, FLamide, and elevenin receptors. We also identified a ligand for the Platynereis ortholog of vertebrate thyrotropin-releasing hormone (TRH) receptors, revealing the ancient origin of TRH-receptor signaling. We predicted ligands for several metazoan GPCRs and tested predicted achatin receptors. These receptors were specifically activated by an achatin D-peptide, revealing a conserved mode of activation. Our work establishes an important resource and provides information about the complexity of peptidergic signaling in the urbilaterian.

Evolutionarily conserved TRH neuropeptide pathway regulates growth in Caenorhabditis elegans

“…Various lines of evidence suggest that they belong to the TRH neuropeptide family. In Platynereis the EFLGamide peptides were recently shown to activate the TRHR ortholog in this species (22). Our results are in line with this study.…”

“…Based on the lack of evidence for TRHR ligands in protostomes, except in Platynereis (22), it was proposed that TRH neuropeptides have been lost in this lineage, or at least in Ecdysozoa (21)(22)(23)53). Our in silico search revealed the presence of TRH-like peptides in nematodes, arthropods, annelids, and mollusks.…”

“…beets@kuleuven.be. including TRH, has been lost in protostomes, at least in the ecdysozoan phyla (arthropods and nematodes) (21)(22)(23)(24) 1B). We challenged receptorexpressing cells with a synthetic library of more than 250 known and predicted C. elegans peptides, but none was able to activate TRHR-1.…”

“…Neuropeptide ligands have been identified for vertebrate and Platynereis TRHRs (22,26). We tested whether TRH-like peptides of these species could activate C. elegans TRHR-1 in cell-culture cells (Fig.…”

“…TRHR orthologs were identified in the annelid Platynereis dumerilii and in the genomes and transcriptomes of mollusks, arthropods, and Caenorhabditis elegans (19-21). However, with the exception of Platynereis and molluscan EFLGamides, no ortholog of the vertebrate TRH precursor was found in any protostomian genome (21,22). Therefore, it has been proposed that the HPT axis of vertebrates,…”